Nonlinear partially saturated control of a double pendulum offshore crane based on fractional-order disturbance observer

The stabilizing control of a double pendulum offshore crane in the presence of matched disturbances, unmatched disturbances and the actuator saturations is a challenging problem. To solve this problem, an anti-swing partially saturated control method is proposed. Specially, a Fractional-Order Disturbance Observer (FODO) is designed to compensate for the matched disturbances and a feedback stabilizing controller is proposed to regulate the hook and cargo to desired positions and suppress swings. Afterwards the closed-loop asymptotical stability is strictly proven. Extensive simulation results are given to demonstrate that the proposed controller could suppress the swing effectively without exceeding the actuator saturations and has strong robustness to various disturbances.